Not according to JS Wrights it isn't.
To be honest I think you are both correct in a round about way.
Air drying - you will never get any moisture trapped because this is a very gentle process (UK climate). BUT you will only ever get down to around 20% moisture but this should be consistent all the way through the cleft.
Kiln drying if done incorrectly will result in a. Moisture trapped in the centre and b. a brittle outer layer.
Kiln drying done correctly will result in a very uniform moisture across all clefts in the kiln and can be very accurately controlled/monitored.